In real life when it rains, snow or any liquid touches the plane it will sit on the wing and maybe fall off the wing in the future. Moisture/rain on the wing can also lead to icing so seeing the transition from liquid on your wing to solid would look really cool. An example of liquid falling off the wing during takeoff. In MSFS any liquid just falls through the wing. SNOWY 737-800 Takeoff after Snowstorm (Taxi, De-ice, Takeoff) - YouTube